Microwave heating can be used to selectively deliver energy to certain types of molecules having dipole moments, such as water; the result of absorption of this energy is an increase in temperature, thus microwaves can be used to heat a portion of a lossy medium, such as the human body. It is also well known that a modest increase in temperature, such as heating to 42-44° C., can cause cancer cells to become much more susceptible to various methods of injuring or killing cells; thus increasing the temperature of a person's body during a cancer treatment can enhance the effectiveness of the treatment. One way to heat cancer cells in vivo is thus to apply microwave energy to the cells, which can be used for hyperthermia.
Since 1980, various hyperthermia methods have been developed to raise the temperature of part or all of the body of a cancer patient. These methods have been used locally (i.e., within a small area, such as directly in tumor tissue), regionally (in a larger portion of the body, such as a particular limb where a tumor is located), and even for the entire body of the patient (whole-body hyperthermia). Local and regional hyperthermia methods attempt to selectively warm a targeted tumor directly, without substantially affecting the rest of the patient's body. Whole-body hyperthermia is often used as a systemic treatment for a cancer condition that is delocalized or has metastasized. These methods have been shown to reduce some of the adverse effects caused by radiation and chemical cancer therapies, and to make these therapies more effective. Recent basic and clinical research shows that whole body hyperthermia may be widely applicable as an adjunct treatment used in combination with conventional chemotherapy and ration treatments, as methods for providing whole-body hyperthermia temperatures improve.
Heating methods used for hyperthermia treatments include exposure to warm air or water, as well as application of heat in the form of electromagnetic radiation, including infrared and microwave radiation. Microwave heating has been most effectively used for localized heating, where various means for focusing the microwave energy in and around the targeted tumor have been used. See, e.g., U.S. Pat. No. 5,571,154. Heated air or water tend to be too slow and uncomfortable for patients to endure. Most of the traditional whole-body hyperthermia devices use infrared (IR) heating technology. For example, ET-SPACE™, one of the whole-body heating apparatus manufactured by ET Medical Corporation of the P.R.China, is a hyperthermia apparatus using infrared radiation to heat a patient's body. This system raises body temperature by exposing the body to specific infrared frequencies. The infrared energy is absorbed at the surface of the skin, and the heated skin gradually transfers the heat to the fat and then to the muscle by conductive heat transfer. The heat is then slowly transferred to the inside of body where it warms the blood, which gradually increases the whole body temperature. Other devices known in the art utilize microwave energy to heat the body of a subject, but are generally designed to focus microwave energy in a local or regional treatment, e.g., U.S. Pat. Nos. 4,586,516; 4,589,423; 4,669,475; 4,672,980; and 4,798,215; and 4,860,752 appear to relate to localized treatment methods, and contemplate ways to utilize interference to focus energy selectively on a tumor to be treated.
However, there are several shortcoming with this type of device:                1. The infrared radiation cannot penetrate the skin, nor does it penetrate the fat or muscle. It relies on heat transfer from the skin, and the skin can only be heated modestly before pain and injury thresholds are exceeded.        2. The skin of a human body can incur severe skin bums when exposed to temperature higher than 46° C. for a long period of time, while muscle and other tissues will suffer if maintained at temperatures above about 43° C. Hence, the temperature inside an infrared treatment chamber can not be over about 45° C. for safety reasons. However, the normal human temperature is around 37° C. This means the temperature difference between the treatment chamber and human body is no more than about 8° C. As a result, heat transfer during such treatments is very slow, which results in long heating time—thus a single IR hyperthermia treatment usually last for 5-6 hours, because the body temperature increases very slowly toward the level where a significant hyperthermia effect occurs. Thus this method risks skin burn and other injuries, and stresses the entire body for a long period of time.        3. It is intolerable for a patient to stay inside an enclosed IR treatment chamber at 45° C. for 5-6 hours, so the patient must be put into deep anesthesia which adds additional stress and risk for the cancer patient, in addition to the stresses caused by the primary radiation or chemotherapeutic treatment that is being used.        4. The reported incidence of adverse effects from heating a subject with the ET-SPACE™ systems is 10.6%, consisting of 2nd degree skin bums and bedsores.        5. The infrared based device has limited application in that it cannot be used to perform regional hyperthermia. Thus a cancer treatment facility must have separate devices in order to provide local/regional hyperthermia treatments and whole-body hyperthermia treatments.        
There is thus a need for improved methods and devices for heating a subject's whole body during hyperthermia treatments. Improved methods and devices should provide at least some of the following advantages: faster heating time, to achieve an effective body temperature more quickly; decreased risk of injuries caused by localized heating; reduced discomfort so that patients may not require prolonged or general anesthesia during hyperthermia treatment; and the flexibility to use a single device for both local/regional treatments and for whole-body hyperthermia treatments. The present invention provides devices and methods that offer such advantages.